1. Field of the Invention
This invention relates to a process for the decontamination of environments contaminated with halogenated organic compounds. In one of its more particular aspects, this invention relates to the microbiological degradation of toxic halogenated organic compounds.
Halogenated organic compounds are used in a wide variety of synthetic and utilitarian applications in industry, agriculture, and health care. For example, halogenated organic compounds are used in dielectric fluids, flame retardants, refrigerants, heat transfer fluids, protective coatings, pesticides and other chemical products. Disposal of these materials after use and halogenated by-products of their production poses a serious problem because of the toxicity of many of these halogenated organic compounds. The disposal of toxic waste has, in recent years, achieved such huge proportions that storage of toxic chemicals in landfills and other areas designated for storage thereof no longer satisfies the ever growing need for safe and efficient disposal of these materials.
2. Prior Art
Many different methods have been proposed for rendering toxic wastes innocuous. Among these are incineration, chemical transformation, and microbiological degradation. Because microbiological degradation of toxic waste does not involve the use of chemical reagents which might themselves be toxic and does not result in the production of large amounts of noxious fumes, such as produced in the incineration of toxic waste, it has become a preferred method of disposing of toxic waste.
Most microbiological degradations of toxic materials are based upon discovering a particular microorganism which will metabolize the toxic material, converting it to innocuous metabolic products, usually, in the case of organic compounds, carbon dioxide, water and salts. Finding microorganisms which can efficiently and safely convert toxic wastes into innocuous metabolic products is a highly complex procedure involving many arduous steps and requiring a significant expenditure of time.
One such procedure is taught in U.S. Pat. No. 4,493,895, wherein is described a process for microbial degradation of obnoxious organic wastes into innocuous materials. This process comprises the steps of (1) collecting a sample of material from the site contaminated with obnoxious chemicals; (2) enriching the microorganisms found living in the sample; (3) separating the strains of microorganisms capable of having different metabolisms for the various chemicals in the sample from the site, from each other; (4) purifying the strains which are capable of biodegrading the chemicals to be disposed of; (5) applying the strain to the locus of the contaminants to be disposed of; and (6) monitoring of removal of the contaminants at the locus of the application. It can be seen that this is indeed an involved procedure requiring large amounts of time and effort.
Another approach taught in U.S. Pat. No. 4,511,657 involves a process of treating chemical waste landfill leachates with activated sludge containing bacteria capable of metabolizing obnoxious organics present in the leachates.
In each of these schemes, dependence is placed upon finding a particular microorganism or microorganism-containing sludge to metabolize the obnoxious organic materials constituting the toxic waste. It would be desirable if, rather than simply adding a particular strain of microorganism to the material to be degraded, it were possible to rely upon the microorganisms already present in the environment, that is, microorganisms indigenous to the environment in question, to accomplish the degradation.
Although various aspects of microbiological degradation of organic compounds have been studied, no solution to the problem of utilizing indigenous microorganisms for metabolizing recalcitrant contaminants has been found.
In "Microbial Degradation of Organic Compounds," David T. Gibson, Editor, P. 362, Marcel Dekker, Inc., New York, 1984, the metabolism of commercial PCB mixtures and biphenyl is discussed, but no commercially suitable process is described.
In "Biodegradation of Pesticides," Fumio Matsumura and C. R. Krishna Murti, P. 70, Plenum Press, New York, 1982 the term "cometabolism" is defined to include cases where the microorganisms are induced by chemicals which structurally resemble the pesticide molecules.
I. S. You and R. Bartha describe the increased mineralization of 3,4-dichloroaniline in the presence of aniline in "Stimulation of 3,4-Dichloroaniline Mineralization by Aniline", Applied And Environmental Microbiology, 44:678 (1982).
D. D. Focht and M. Alexander describe the cometabolism of various organic compounds structurally related to DDT in "DDT Metabolites and Analogs:Ring Fission by Hydrogenomonas", Science, 170:91 (1970).
While these references teach the cometabolism of potentially contaminating organic compounds, no practical process for degrading chlorinated organic compounds in a natural environment is taught.
Cometabolism is reviewed by Raymond S. Horvath in "Microbial Co-Metabolism and the Degradation Of Organic Compounds In Nature", Bacteriological Reviews, 36:146 (1972).
R. S. Horvath and P. Flathman in "Co-Metabolism of Fluorobenzoates by Natural Microbial Populations", Applied And Environmental Microbiology, 31:889 (1976) describe the oxidation of fluorobenzoic acids by microorganisms which could not utilize these compounds as sole sources of carbon and energy in a basal salts medium and required the addition of glucose to sustain cell growth.
K. Furukawa, N. Tomizuka, and A. Kamibayashi in "Metabolic Breakdown of Kaneclors (Polychlorobiphenyls) and Their Products By Acinetobacter sp.", Applied And Environmental Microbiology, 46:140 (1983) describe the utilization of strains of Acinetobacter to metabolize commercial mixtures of polychlorobiphenyls and deduce a pathway for such metabolism.
None of the prior art discloses a commercially useful process for the decontamination of environments contaminated with halogenated organic compounds. None of the references teaches how non-indigenous microorganisms specifically adapted for the metabolism of the contaminant can be utilized with microorganisms indigenous to the environment to accomplish decontamination at a rate which is within practical limits.
It is accordingly an object of the present invention to provide a process for the decontamination of environments contaminated with halogenated organic compounds.
It is another object of the present invention to utilize microorganisms indigenous to such environments in the decontamination thereof.
Another object of this invention is to provide a process whereby the rate of decontamination of such environment can be accelerated.
Other objects and advantages of the present invention will become apparent in the course of the following detailed description.